A survey of the ECG changes in 1906 cases in three districts of Okayama Prefecture was conducted over the past 10 years with particular emphasis on those exhibiting Minnesota Code 1-0. 1) Of the 741 cases which were ECG Code 1-0 in 1966, 77.1 % remained Code 1-0 in 1970 and 57.2 % in 1976. 2) Many cases which were initially ECG Code 1-0 in 1966 but with concomitant high blood pressure had changed to Code 3, Code 3+4+5, or Code 3+5 during the next 10 years. 3) Females constituted most of the Code 4+5 and Code 5 patients. 4) Those with Code 1-0 in 1966 and normal blood pressure, urinalysis and other physiological parameters dropped to 84.9 % in 1976. 5) In those cases which remained Code 1-0 for 10 years, no significant changes were noted in the QT-interval, PR-interval, QRS-complex, or the size of the T-wave of their ECGs. 6) Among the 66 cases which were initially ECG Code 3 (only 1 subcode) in 1966, some had progressed to Code 3+4+5 or Code 3+5 and some had returned to Code 1-0 by 10 years later. It was concluded that aging has very little effect on the ECG. Other factors appear to be more important in causing ECG changes.